Process for solvent extraction of oils



Nov. 30, 1937.

U. B. BRAY PROCESS FOR soLvENT EXTRACTION 0F OILS Filed April lO, 1934 INVENTOR. Z/rzc 5.52273 ATTORNEY.u

Patented Nv. 3o, 1937 UNITED STATES PATENT OFFICE Ulric B. Bray, Palos Verdes Estates, Calif., as-

signor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application Aprlllo, 1934, Serial N0. '719,910

11 Claims.

This invention relates to the extraction of oils' by employing a selective solvent. Although applicable to the treatment of other oils, it refers more particularly to the production of lubricat- 5 ing oil by a selective solvent extraction process.

It has been found that desirable parafiinic hydrocarbons can be separated from the undesirable olelnic, naphthcnic and/or aromatic compounds by the use of solvents which selectively dissolve the undesirable hydrocarbons but which exhibit only a very limited solvent power upon the desirable paraiimic hydrocarbons. When I use the te'im paramnic hydrocarbons I mean those highly saturated compounds which l5 are present in petroleum and which are characterized by a low temperature viscosity susceptibility, i. e. they exhibit a minimum change in viscosity for a' given change in temperature. ,1 They also are characterized by relative stability jg to air and sunlight, exhibiting little tendency to-4 ward discoloration or sludge formation. This definition is not meant to include those compounds which are usually solid or semi-solid at ordinary temperatures and which are known as 35 wax or petrolatum; but, of course, it is obvious that my invention is meant to also include the selective extraction of waxy oils. As a matter of convenience hereafter, I will refer to the undesirable components, such as oleflnic, naph- 30 thenic and/or aromatic hydrocarbons, as the non-paraiiinic components of petroleum.

These fractions are characterized by a relatively high temperature viscosity susceptibility and are relatively unstable to air and sunlight, exhibiting gil', discoloration and sludge formation.

A further indication of the purity of a lubricating oil is its viscosity gravity constant. This constant represents the paraiiinicity or naphthenicity of an oil. A high value represents a 40 high degree of naphthenicity while low values indicate relatively greater paraiiinicity. Lubricating oils from natural crudes range from 0.903 viscosity gravity constant for an extreme Gulf Coast type to 0.807 for an extreme Pennsylvania i5 type or even beyond. The viscosity gravity constants referred to in this application have been determined by the method employed by Hill and Ccates as set forth in the Journal of Industrial and Engineering Chemistry, vol. 20, page 641 of 50 1928. The paranc hydrocarbons to which I refer hereinafter are characterized by relatively low viscosity gravity constant, while the nonparainic constituents of petroleum are characterized by relatively high viscosity gravity con- 55 stant.

A number of selective solvents for extraction have been found; for example, it has been shown that such materials as anlline, chloraniline, nitrobenzene, dichlorethyl ether, phenol, chlorophenol, cresol, sulphur dioxide commingled with benzene, and furfural are highly selective as solvents for the non-parailinic hydrocarbons. When these solvents are commingled with petroleum or petroleum fractions under the proper conditions of temperature, the undesirable non-parafiinic hydrocarbons pass into solution to a greater or less extent but a substantial proportion of the desirable paramnic hydrocarbons remains undissolved. The solution of undesirable hydrocarbons and solvent settles to the bottom of the container and forms an extract phase when relatively heavy solvents are employed. The relatively light paraiiinic hydrocarbons rise to the top of the vessel and form a rainate phase. These phases are then readily separable by ordinary decantation means. The raiiinate phase is usually found to contain a small quantity of the selective solvent and the extract phase ordinarily contains a relatively large quantity of the solvent. These fractions may be puried by distillation whereby the solvent is distilled away from the hydrocarbon oils.

In the usual solvent extraction of mineral oil with selective solvents, such as those above mentioned, the separation is not complete. Particularly, all of the parainic hydrocarbons, i. e. the more valuable lubricants, are not obtained in the raii'inate phase but instead some oi' the high grade parailinic oil fractions are found in the extract phase. Due to the similarity of the various hydrocarbon components of mineral oil fractions, such as lubricating oils, the solubility of the undesirable non-parainic fractions and the desirable parafllnic fractions in a selective solvent usually differ only in degree and there is, therefore, a tendency for desirable high grade parailinicv oils to be carried away with the extract resulting in a loss in the yield of paramnic fractions obtained. In other words, in a phase separation of extract and raiilnate fractions from mineral oil by employing a selective solvent, an equilibrium ofparaiiinic components and nonparafnic components is established between the phases. Consequently some of the desirable paraflinic fractions are found in the extract instead of in the railinate. 1

The solubility of oils of relatively high paraflinicity in the extract phase can be reduced by the presence of an anti-solvent with the oil during extraction with a selective solvent. An antisolvent may be dened as a material which tends to prevent the solution of those hydrocarbon fractions which, except for the presence of the anti-solvent, would be dissolved in the extract phase upon extraction of the oil with a selective solvent. When, during extraction, an antisolvent is introduced into that zone wherein some of the oil of relatively high parafllnicity is dissolved in the solvent, this valuable oil is rejected from solution and is recovered in the raffinate phase. When, before extraction, an anti-solvent is commingled with the oil to be extracted, the solution of oil of relatively high paraii'lnicity in the extract phase is inhibited.

It is an object of this invention to extract oil with a solvent in the presence of an anti-solvent to force into the raffinate phase that portion desired in the rafnate which would otherwise remain in the extract phase.

'I'he anti-solvent which I may employ is preferably one which is adapted to form a two phase system with the raffinate produced by the extraction and is soluble in the extract phase. As an anti-solvent having these characteristics, I may employ liquid ammonia, oreven water may be used as an anti-solvent when the water forms a solution with the selectivesolvent with which it is employed.

Under certain conditions, the anti-solvent may be a substance which is a selective solvent when employed alone. For instance, the anti-solvent may be a selective solvent which has less solvent power than the selective solvent employed in the extraction. As an example, the extraction may be accomplished by a selective solvent such as chloraniline or a mixture of liquid sulphur dioxide and benzene, characterized by high solvent power for higher grade material. The anti-solvent which I may use may be liquid sulphur dioxide or other solvent having relatively less solvent power for the higher grade material.

When oil is countercurrently extracted with a selective solvent and when an anti-solvent of the type dened above is commingled with the oil prior to extraction or is introduced into that zone of the extraction into which fresh oil to be extracted is also introduced, I have found that the anti-solvent tends to diffuse through the solvent, being soluble therein, in such manner that the proportion of anti-solvent to solvent l.decreases between the point of introduction of the anti-solvent and the point of removal of the rainate from the extraction. If, for instance, the solvent is introduced into the top of an extraction column and the oil and anti-solvent are introduced together in the bottom, the top portion of the column contains solvent of relatively high solvent power whereby an extract phase is produced therein comprising some fractions of relatively high parailinicity. As the extract phase descends through the column, it contacts with anti-solvent which is present in successively increasing proportions whereby thek oil of relatively high paraflinicity is rejected from the extract phase and travels upwardly for recovery with the final raiiinate.

It is a further object of my invention to countercurrently extract oil with a selective solvent and to introduce into that zone of the countercurrent extraction to which oil entering said extraction is introduced an -anti-solvent adapted to form a two phase system with the rafllnate and to be soluble in the extract phase whereby the extraction is accomplished by a selective solvent of successively decreasing solvent activity.

Another type of anti-solvent is one which is substantially soluble in the raflinate phase. Anti-solvents having this characteristic are,l for example, liquid, normally gaseous hydrocarbons such as liquid ethane, propane, or butane, methyl cellosolve (mono-methyl ether of ethylene gly` col), carbitol (mono-ethyl ether of di-ethylene glycol) and other oxygenated compounds such as acetone or methyl acetate. Anti-solvents of this type may be employed if desired, together with the previously mentioned anti-solvents which are adapted to form a two phase system with the raillnate produced by the extraction and which are soluble in the extract phase.

The gure is a schematicA arrangement of one form of apparatus which may be employed to carry out my process.

Referring to the figure, oil enters extractor I8 by action of pump II in line I2 controlled by valve I3. The anti-solvent which forms a two phase system with the raffinate produced by the extraction and which is soluble in the extract phase, passes by action of pump I4 through line I5 controlled by valve I6 into line I2 to commingle with the oil travelling therethrough. Preferably, the oil and anti-solvent are introduced into the lower portion of extractor I0 for countercurrent extraction with selective solvent introduced into the upper portion thereof by action of pump I1 in linel controlled by valve I9. Finished railnate is removed from extractor I0 via line 2l! controlled by valve 2I. Extract phase is removed from extractor III by action of pump 22 in line 23 controlled by valve 24.

If desired, the extract phase passing through line 23 may enter separator 21 to commingle therein with an anti-solvent introduced by action of pump 28 through line 29 controlled by valve 30. 'I'he anti-solvent which enters via line 29 is preferably one which is substantially soluble in the raiiinate phase. Accordingly.- an intermediate railinate is rejected from the extract phase in 21. Extract phase is removed from separator 21 via line 3| controlled by valve 32.

When the extract phase from extractor III is commingled with an anti-solvent` in separator 21 the solution of rejected intermediate raflinate and anti-solvent issues from 21 by action of pump 33 in line 34 controlled by valve 35. This mixture can be introduced into line I2 to commingle with fresh oil brought to extractor I Il when valves 36 and 31 are open in line 34 and valves 38 and 39 are closed in lines 40 and 4I, respectively. In'

some cases it may be desired to introduce this solution into extractor III withoutv commingling with fresh oil introduced therein. In this event, the solution may pass through line 34, valves 35 and 35 and valve 39 and line .4I, valves 31 and 38 being closed. When it is desired to remove antisolvent associated with the rejected intermediate raflinate passing through line 34, valve 36 may be closed in order to cause the mixture to pass via line 40 and valve 38 into heater 42 and thence through line 43 into separator 44 wherein the anti-solvent vapors are removed by passage through line 45 controlled by valve 46. The rejected intermediate rainate freed from antisolvent then passes by action of pump 41 through line 48 controlled by valve 49 into cooler 50 and thence may travel either through line 4I into extractor I0 or through valve 31 to commlngle with fresh oil passing through I2.

As one example of the operation of the above described apparatus, oil characterized by a viscosity gravity constant of 0.875 may be intro- Cil duced into extractor I 0 via line I2 together with 10 volume percent. of water introduced via lines I5 and I2. The oil may be extracted with 200 volume percent. ortho-chlorophenol introduced via line I8. The raffinate issuing via line 20 is characterized by a viscosity gravity constant of 0.810 and is obtained in 40% yield. When the same oil is extracted under the same conditions with ortho-chlorophenol in the absence of the anti-solvent, the raffinate issuing through 20 has about the same viscosity gravity constant but the yield is only 28%, indicating that the anti-solvent reduces the loss of fractions of relatively high paraillnicity in the extract phase.

By introducing the water either commingled with the oil entering the lextraction or by introduction of the water into the same zone in which the fresh oil enters the extractor, the proportion of anti-solvent to solvent is greatest at approximately that point at which the fresh oil is introduced. As previously stated, this anti-solvent is soluble in the extract phase and d ue to the counterilow of materials and to the agitation in extractor I0, the anti-solvent tends to diifuse through at least a portion'of the extractor and to be present in successively decreasing amounts as the oil ascends the column. Consequently, the solvent in the upper portion of the column may be substantially unmodified by anti-solvent, and due to the high solvent action of this solvent the extract phase will comprise some fractions of relatively high parailinicity desired in the rafnate phase. This extract phase descends through the column and passes through zones of increasingly larger proportions of anti-solvent whereby the solvent power of the selective solvent is successively decreased in the column and the fractions of relatively high parainicity are rejected from the extract phase for recovery in the raftinate passing through line 20.

If desired, both types of anti-solvent may be introduced with the oil entering through line I2, e.,g. the oil may be commingled with an antisolvent such as liquid propane to the extent of 400 volume percent. and with water or anhydrous liquid ammonia or the like, to the extent of 12 volume percent. In this case the solvent, such as ammonia, which is adapted to form a two phase system with the raffinate and which is soluble in the extract phase functions in the above described manner for passage of .the extract phase through zones of increasing proportion of antisolvent. While the other type of solvent, e. g. liquid propane, which is substantially solub`.e 'in the raflinate phase travels upwardly through c cjlumn I0 and is discharged with the railinate.

As another example, oil characterized by a viscosity gravity constant of 0.872 intermixed with 300 volume percent. liquid sulphur dioxide, enters extractor I0 via line I 2 for countercurrent extrac' tion with 250 volume percent. of a solvent comprising '70 volume percent. liquid sulphur dioxide and 30 volume percent. benzene. issuing through line 20 is characterized by a viscosity gravity constant of 0.808. The extract phase issuing through line 23 having a viscosity gravity constant of 0.890 is introduced into separator 21 for intermixture with liquid propane to the extent of 400 volume percent., based upon the volume of oil introduced into the system via line I2. The material passing through line 34 comprises a solution of liquid propane and intermediate rafnate rejected from the extract phase in separator 21. This mixture is passed by line 34 into line I2 for further extraction in extractor The raffinate.

I 0. Extract removed via line 3l has a viscosity gravity constant o! 0.941. The presence of liquid sulphur dioxide introduced by line I2 into extractor I0 causes the extract phase produced by countercurrent extraction with the mixture of liquid sulphur dioxide and benzol to descend through zones of relatively increasing proportions of liquid sulphur dioxide in relation to the benzol whereby the activity of the solvent is successively reduced causing rejection of fractions of relatively high paramnicity from the extract phase as the extract proceeds from the upper to the lower portion of extractor I0. The liquid propane introduced through line 29 and passing with the reiected intermediate ramnate through line 34v travels upwardly through extractor I0 and issues therefrom'with the raiilnate via line 20.

As previously stated, when an intermediate ramnate is rejected i'roml the extract phase by means of an anti-solvent soluble in the rejected intermediate ramnate, the solution of rejected intermediate raiiinate and anti-solvent passing through line 34 may be commingled with fresh feed and anti-solvent passing through line I2or it may be introduced into the extraction without first mixing with'the fresh feed of oil, for instance, by passage through line 4I. Also, the anti-solvent can be removed from the rejected intermediate ramnate by distillation or the like before the rejected intermediate raillnate is re turned to the extraction.

It isv to be understood that the foregoing is merely illustrative of the generic invention and that the examples are not to be taken as limiting thereof as many modifications of my invention may be made within the scope of the following claims.

1. A process for the solvent extraction of oil by a selective solvent into an extract phase comprising oil dissolved in said solvent and a rafnate phase substantially insoluble in said solvent which comprises commingling with the oil to be extracted an anti-solvent soluble in said extract phase and adapted to form a two phase system with the railinate and countercurrently extracting said mixture with said selective solvent, separatingl extract phase from railinate phase and rejecting an intermediate raffinate from said extract phase by commingling said extract phase with an anti-solvent substantially soluble in said rejected intermediate raflinate.

2. A process for the solvent extraction of oil by a selective solvent into an extract phase comprising oil dissolved in said solvent and a rafiinate phase substantially insoluble in said solvent which comprises commingling with the oil to be extracted an anti-solvent which is soluble Y' in said extract phase and adapted to form a two phase system with the raiiinate, countercurrently extracting said mixture in an extraction system with said selective solvent, separating extract phase from raffinate phase, commingling said extract phase with an anti-solvent to reject an intermediate rafiinate therefrom and returning said rejected intermediate rath-nate to said extraction.

3. A process for the solvent extraction of oil by a selective solvent into an extract phase comprising oil dissolved in said solvent and a rafilnate phase substantially insoluble in said solvent which comprises commingling with the oil to be extracted an anti-solvent which is soluble in said extract phase and adapted to form a two phase system with the rafiinate, countercuri phase substantially insoluble in said solvent which comprises commingling with the oil to be extracted an anti-olvent which is soluble in said extract phase and adapted to form a two phase system with the raffinate, countercurrently extracting saidmixture in an extraction system with s'aid selective solvent, separating extract phase from raffinate phase, rejecting an intermediate rafllnate from said extract phase by commingly said lextract phase with an anti-solvent substantially soluble in said rejected intermediate raillnate and returning said rejected intermediate railinate into said extraction.

`5. A process for the solvent extraction of oil by a selective solvent into an extract phase comprising oil Adissolved in said solvent and a rafnate phase substantially insoluble in said solvent which compries commingling with the oil to be extracted an anti-solvent soluble in said extract phase and adapted to form a two phase system with the raiiinate, countercurrently extracting said mixture in an extraction system with said selective solvent, separating extract phase from raffinate phase, rejecting an intermediate railinate from said extract phase by commingling said extract phase with an anti-solvent substantially soluble in said rejected intermediate rafnate and commingling said rejected intermediate railinate with fresh oil being introduced into said extraction.

6. A process for the solvent extraction of oil 'by a selective solvent into an extract phase comprising oil dissolved in said solvent and a raiilnate phase substantially insoluble in said solvent which comprises commingling with the oil to be extracted an anti-solvent soluble in said extract phase and adapted to form a two phase system with the railinate, also commingling said oil to be extracted with an anti-solvent substantially soluble in said raillnate phase and extracting said mixture with said selective solvent.

7. A process for the solvent extraction of oil by a selective solvent into an extract phase comprising oil dissolved in said solvent and a raiiinate phase substantially insoluble in said solvent which comprises commingling with the oil to be extracted an anti-solvent which is soluble in said extract phase and adapted` to form a two phase system with the raffinate, countercurrently extracting said mixture in an extraction system with said selective solvent, separating extract phase from raiiinate phase, rejecting an intermediate rafllnate from said extract phase by commingling said extract phase with an antisolvent substantially soluble in said rejected intermediate raflinate, removing said anti-solvent from said rejected intermediate raiiinate and introducing said rejected intermediate raninate into said extraction.

8. A process for the 'solvent extraction of oil by aselective solvent into an extract phase comprising oil dissolved in said solvent and a railinate phase substantially insoluble in said solvent which comprises commingling with the oil to be extracted an anti-solvent which is soluble in said extract phase 4and adapted toform a two phase system with the ratlinate, countercurrently extracting said mixture in an extraction system with said selective solvent, separating extract phase from raflinate phase, rejecting an intermediate raffinate from said extract phase by commingling said extract phase with an anti-solvent substantially soluble in said rejected intermediate rainate, heating said solution of anti-solvent and rejected intermediate railinate to vaporize the anti-solvent, cooling the intermediate raftinate freed from anti-solvent and introducing said rejected intermediate rainate into said extraction.

9. A process for the solvent extraction of oil by a selective solvent into an extract phase comprising oil dissolved in said solvent and a raftinate phase substantially insoluble in said solvent which comprises commingling with the oil to be extracted an anti-solvent which is soluble in said extract phase and adapted to form a two phase system with the railnate, countercurrently extracting said mixture in an extraction system with said selective solvent, separating extract phase from raffinate phase, rejecting an intermediate rainate from said extract phase by commingling said extract phase with an anti-solvent substantially soluble in said rejected intermediate raiiinate, removing anti-solvent from said rejected intermediate railinate and commingling said rejected intermediate ramnate freed from anti-solvent with fresh oil being introduced into 1 said extraction system.

10. A process for the separation of oil containing paraflinic and non-paraiiinic constituents,

into fractions relatively more paraiiinic and fractions relatively less paraflinic than the original oil which comprises, commingling said oil with a selective solvent for the relatively less parafnic oil fractions and thereby forming a rainate phase containing the relatively more paraillnic oil fractions and an extract phase containing the relatively less paraiinic oil fractions dissolved in the selective solvent, separating said phases, contacting the extract phase with a liquefied normally gaseous hydrocarbon and thereby dissolving the relatively more paramnic oil fractions 

